1. Field of the Invention
The present invention relates to a technique for manufacturing a semiconductor device, and in particular, to a character pattern extracting method, a charged particle beam drawing method, and a character pattern extracting program.
2. Description of the Related Art
In a charged particle beam drawing method, a variable shaping beam (VSB) scheme which draws a circuit pattern on a resist film by a rectangular beam shaped by using two apertures is a mainstream scheme. In contrast to this, a character projection (CP) scheme is examined which draws a circuit pattern on a resist film by a beam shaped by using a CP aperture. The CP aperture is provided with a character pattern that is similar to some of circuit patterns to be manufactured. A large number of character patterns are formed in the CP aperture to make it possible to shorten drawing time of a circuit pattern. However, the number of character patterns which can be formed in the CP aperture is limited.
Therefore, in a prior art, a plurality of character patterns are prepared, a maximum number of character patterns which can be formed in a CP aperture are selected from the number of prepared character patterns, and a plurality of combinations of the selected maximum number of character patterns are created. Furthermore, the drawing time of a circuit pattern when the plurality of combinations are created in a CP aperture is predicted, and a character pattern included in a combination the drawing time of which is shortest is set in an actual CP aperture (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 7-307262). However, a long time is required to predict the drawing times of the plurality of combinations selected from all the character patterns. Consequently, the time for designing a CP aperture becomes disadvantageously long.